Vasopressin regulates the transfer of water and solutes across the epithelial cells of the mammalian collecting duct and the toad urinary bladder, increasing the permeability of the membrane. Biochemical techniques will be used to characterize alterations in properties of toad bladder epithelial cell plasma membrane brought about by hormone. Luminal plasma membrane glycoprotein(s) associated with vasopressin-sensitive urea flux will be further isolated and characterized. The luminal surface of the intact tissue will be treated with reporter molecules, lectins, crosslinking agents, enzymes and fluorescent probes. Their effects on transport will be measured in the presence and absence of hormone, to describe how vasopressin at the serosal surface alters the luminal plasma membrane disposition of protein, glycoprotein and lipid as it increases transport. Conformational changes in luminal plasma membrane proteins and the state of liquidity of the hydrophobic phase will be assessed using fluorescence spectroscopy of covalently bound extrinsic fluorophores, in both the intact bladder and in plasma membrane fragments. The two major cell populations of the epithelium will be separated and attempts made to subdivide the anatomically homogenous population on a functional basis. The hormone-receptor interaction will be characterized in the intact cell.